1. Field of the Invention
The present invention relates to a laser processing device configured to change a distance between a processing nozzle and an object to be processed.
2. Description of the Related Art
Generally, laser processing is carried out while executing gap control for maintaining a distance (gap) between an object to be processed (or a workpiece) and a processing nozzle for irradiating a laser beam at a predetermined value. As an example of the gap control, JP 2000-343255 A discloses that a gap sensor is arranged on a nozzle in order to detect the distance between the nozzle and a workpiece, and a profile control is carried out based on a signal from the gap sensor.
In the gap control, when a processing nozzle approaches a workpiece, a gap sensor for detecting a gap between the nozzle and the workpiece continues to output a maximum value until a surface of the workpiece enters a detection range of the gap sensor. On the other hand, the velocity of a control axis (such as an axis for driving the processing nozzle) for controlling the gap is normally calculated from a detection value of the gap sensor and a gain setting value for determining a motion velocity. In this regard, the gain is set to a relatively high value during the approach motion of the nozzle, since the approach motion must be at high speed. Otherwise, until the processing nozzle is moved or lowered to a certain height position in the vicinity of the surface of the workpiece, the processing nozzle may be rapidly lowered at an approach motion velocity determined without depending on the detection value of the gap sensor (i.e., the approach motion velocity is higher than the velocity calculated from the sensor detection value and the gain setting value).
However, if the approach motion velocity is high, even when the control axis of the processing nozzle is decelerated after the existence of an obstacle between the processing nozzle and the workpiece is detected or after an abnormality (such as excess inclination or warpage) of the workpiece is detected, the processing nozzle may collide or interfere with the obstacle, etc., and may be damaged.
In the technique of JP 2000-343255 A, the sensor detects the processing nozzle approaches the surface of the workpiece during the approach motion, and the gain for the gap control motion is switched between before and after the approach of the processing nozzle (in other words, the gain is maintained to a relatively high value before the processing nozzle approaches the workpiece, and the gain is decreased as the nozzle gets closer to the workpiece). However, the technique of this document is intended to reduce an approach motion time of the processing nozzle. Although this document describes that it is detected that the nozzle approaches the workpiece, a means for avoiding interference between the nozzle and the workpiece is not considered. Further, an actual mechanical position of a nozzle axis based on an output from a position detector is not considered in this document.